The present invention relates to a developer storage apparatus, a developer cartridge and a developing device employed in an image forming apparatus using electrophotographic process.
A conventional electrophotographic printer has a detachable toner cartridge for storing a toner. The toner cartridge supplies the toner to a developing unit. The developing unit develops a latent image formed on a surface of a photosensitive drum (i.e., an image bearing body) using the toner. The developed toner image is transferred to a printing medium by a transferring unit, and is fixed to a printing medium by a fixing unit. Then, the printing medium to which the toner image is fixed is ejected outside the printer.
After the toner image is transferred to the printing medium, a small amount of the toner may remain on the surface of the photosensitive drum. Such a residual toner is removed from the surface of the photosensitive drum by a cleaning unit. The removed toner (i.e., a waste toner) is collected in a waste toner collection chamber. Generally, the waste toner collection chamber is provided separately from a toner storage chamber that stores a fresh toner. For example, Japanese Laid-open Patent Publication No. 2000-181224 discloses a toner cartridge including a toner storage chamber that stores a fresh toner, and a waste toner collection chamber that stores the waste toner removed from the surface of the photosensitive drum.
The color electrophotographic printer has four developing units of four colors, and the developing units have respective toner cartridges. The above described waste toner collection chamber is provided in one of the four toner cartridges (for example, a black toner cartridge). The waste toners collected from the four developing units are stored in the waste toner collection chamber. With such a configuration, it is not necessary to provide a waste toner collection chamber in other three toner cartridges.
Recently, there is a need for a developer storage apparatus capable of efficiently storing a developer such as a waste toner.